PDO :: errorInfo（）：Array（[0] => 00000 [1] => [2] =>）

I'm using pdo code to process my multilevel users login on my page and got this error after testing:

PDO::errorInfo(): Array ( [0] => 00000 [1] => [2] => )

I have checked my code many times and still can't figure out any mistake. I would appreciate if anyone could explain the error and point out if there are any mistake in my code here:

<?php    
include("db.php"); 
    session_start();
    if (isset($_POST['submit'])){
          $user=$_POST['username'];
          $pass=$_POST['password'];
    $conn->setAttribute(PDO::ATTR_EMULATE_PREPARES,false);
          $query=$conn->prepare("select * from users where username=:user and password=:pass");
          $query->BindParam(":user",$user);
          $query->BindParam(":pass",$pass);
          $query->execute();
          if ($query->rowCount()>0){
                session_start();
                $data=$query->fetch();
                if($data['position']=="kc"){
                      $_SESSION['username']=$data['username'];
                      $_SESSION['position']=$data['position'];
                      header('location:index.php');
                }else{
                      $_SESSION['username']=$data['username'];
                      $_SESSION['position']=$data['position'];
                      header('location:index.php');
                }
          }
          else{

                echo "
PDO::errorInfo():
"; 
                print_r($conn->errorInfo()); 
          }
    }
    ?>